In petroleum refining and storage facilities quantities of hydrocarbon-laden sludge or waste collects in processing equipment or tanks and must be removed periodically as part of routine plant maintenance. Common sources of sludge in the petroleum industry include fuel storage tanks, handling equipment, contaminated bottoms from separators, residue from catalytic processes, spent clays and acids, emulsified liquid-solid materials, sludge from decanting operations, and the like. In the storage of liquid fuels, such as leaded gasoline, various reactions or physical conditions may cause precipitation of hazardous solids to the bottom of storage tanks. Although the precise causes of sludge formation are not completely understood, oxidation, moisture condensation and the like may contribute to formation of a layer of lead-containing material which is removed from the collection point, often by scraping and washing with water and/or cleaning compositions.
Handling of solid refinery waste materials is a difficult problem due to numerous factors such as the diversity of waste, contamination of wastes with oil, water, solvents, etc. The high capital and operating costs of treatment and disposal make such processes expensive. Because of the need for environmental improvement, however, it is necessary that waste treatments and controls be included in manufacturing and industrial processing and there is an obvious need for improved waste disposal techniques. A particular problem within the petroleum industry with respect to the handling of wastes has been the separation and disposal of solid waste materials. In many instances oil containing solids must be separated from oil containing liquids (e.g., emulsions of oil in water and water in oil) and after such separation, the oil containing liquids are difficult to dispose without pollution or they must be specially treated to separate and recover oil therefrom.
It is known in the art that refinery oil sludge materials may be subjected to the action of soil bacteria whereby the oil is decomposed over a period of time. The use of a sand filter to separate oily particles from aqueous emulsion is disclosed in British Pat. No. 1 340 931. In U.S. Pat. No. 3,835,021 (Lorenz et al) a process is disclosed for dewatering and deoiling refinery sludges in a filter press and applying the solid filter cake to soil for biodegradation. In the 1975 American Petroleum Institute "Guide for Controlling Lead Hazard Associated with Tank Entry and Cleaning" sludge disposal by dumping in an exposed pit, ground or concrete surface is discussed. However, the prior disposal procedures are unacceptable for adequate treatment of hazardous wastes, such as hydrocarbon-laden, lead-containing sludge materials. In some prior disposal processes the sludge materials from the refinery were taken directly to a land receptacle and worked into the soil. Where oil was recovered from the sludge materials, the technique used was to bring the oily sludge and emulsions from the refinery to the land area by vacuum truck and discharge them into an enclosed area where they were allowed to spread to a depth of about 6 inches. After settling, the oil which separated to the top was recovered by the vacuum truck for return to the refinery and the remaining sludge was mixed with soil by bulldozer. Such a technique is not only very inefficient with respect to oil recovery, but also actually contributes to pollution because run-off waters from rain on the raw sludge carry away oil and cause oil contamination of streams.
Other sludge filtering techniques are disclosed in U.S. Pat. No. 4,260,489 (Greig et al) wherein the filtration residue is further treated by solvent extraction and/or steam stripping.
Alternatively, the sludge materials may be removed from the refinery site for environmentally safe disposal at approved location; however, this can be a costly procedure and may only defer the detoxification problem. A need exists for on-site treatment of such sludge materials and it is an object of the present invention to provide equipment and processes for recovering and detoxifying hazardous sludge materials.